Typically I get one spam email per day in my spam folder and check about once a month for anything that I may have missed. Recently, it's suddenly about fifty spam emails per day.
I can't find my email address in any search engines or in any forums. Have I Been Pwned lists my email in only two breaches from years ago.
What causes something like this?
I kind of like the darknet monitoring from one of my credit cards. It lists the date and what data was released.
Once it gets too bad, burn the address, forward all mail to a new one, and slowly migrate everything.